1. Technical Field
This disclosure relates to a display device for displaying a video by means of liquid crystal.
2. Description of the Related Art
Techniques for displaying a video by driving liquid crystal have been widely applied to display devices. A liquid crystal display device generally includes a display surface formed of pixels and a backlight device for emitting light toward the display surface. Typically, each of the pixels includes a red sub-pixel with a color filter corresponding to a red hue, a green sub-pixel with a color filter corresponding to a green hue, and a blue sub-pixel with a color filter corresponding to a blue hue. Light from the backlight device passes through these color filters and is emitted as a red light, a green light and a blue light from the display surface. Consequently, a video is displayed on the display surface.
Japanese Patent Publication H11-295717 A discloses techniques for enhancing luminance of a video. According to Japanese Patent Publication H11-295717 A, the display surface is formed with pixels, each of which has a sub-pixel provided with a transparent layer in addition to the aforementioned sub-pixels. Such a sub-pixel with the transparent layer functions as a white sub-pixel which emits white light to brighten a displayed video on the display surface. The techniques disclosed in Japanese Patent Publication H11-295717 A, however, face a problem that it requires additional processes to form the transparent layer.
Japanese Patent Publication 2011-100025 A proposes formation of a through-hole in one of the red, green and blue color filters, instead of forming the transparent layer. The techniques according to Japanese Patent Publication 2011-100025 A allows more simplified formation of the white sub-pixel than the disclosed technologies in Japanese Patent Publication H11-295717 A.
The aforementioned techniques for enhancing luminance by means of four sub-pixels face various problems. For example, the aforementioned techniques result in increased numbers of source driver pins, source lines and TFTs in comparison with typical RGB systems. This, in turn, leads to an increase in manufacturing costs of the liquid crystal display devices.
The increase in the number of sub-pixels means downsized sub-pixels. For example, the aforementioned techniques have to use sub-pixels, each of which has a size “¾” times as large as a sub-pixel size formed according to typical RGB systems.
If luminance under light emission from the red, green and blue sub-pixels is expressed as a value of “1” and if luminance of the white sub-pixel emitting white light is also expressed as a value of “1”, theoretical luminance achieved by the aforementioned techniques is “1.5” times as high as luminance achieved by typical RGB systems (“1” (RGB light emission)×“¾”+“1” (W light emission)×“¾”=1.5).
However, downsizing the sub-pixels and increasing the numbers of source lines and TFTs result in a decrease in an aperture ratio of the sub-pixels (i.e., a light transmission area of the sub-pixels). As a result of the decrease in aperture ratio, the aforementioned theoretical increase in luminance may not be attained.
Technologies to form openings in color filters may degrade video. For example, the opening formed in the color filter may make response speed of liquid crystal slower and cause lower luminance.
It is required for the size of the opening formed in the color filter to be adjusted appropriately in terms of transmittance and color reproducibility. If color reproducibility is important, it may be preferable to form small openings in color filters. In this case, optimal adjustments to color temperatures of backlight and pixel sizes are further required because other portions of the color filter than the openings cause color shifts. If a blue color filter, for example, is formed with an opening, a large red sub-pixel and a large green sub-pixel are required in order to make the remainder of the blue color filter less influential. In addition, the blue color filter has to be small. Therefore, the formation of openings in color filters requires complicated designs for pixels.